Various systems and methods have been suggested for treating spinal disorders, such as degenerative discs, stenosis, trauma, scoliosis, kyphosis, or spondylolisthesis. For example, U.S. Pat. No. 5,545,166, discloses a spinal fixation system that includes a plurality of anchor screws, clamp assemblies, pivot blocks, clamp blocks, and rods that are implanted along a patient's spine to fix two or more adjacent vertebrae relative to one another. The system generally includes a swing bolt anchor screw, a pivot block receivable on the swing bolt, and a clamp block receiving a rod therethrough that is pivotally attachable to the pivot block. In addition, the system includes one or more fixed anchor screws, and clamp assemblies for receiving the rod therein. The clamp assemblies and pivot block are receivable on the anchor screws by spindles that thread along a threaded portion of the anchor screws.
During use, vertebrae to be treated are surgically exposed, and an arrangement of anchor screws and clamp accessories are selected. For example, a fixed anchor screw may be screwed into each of the vertebrae on either side of a first vertebra. A rod is selected that may extend between the fixed anchor screws and that may be bent to conform to the shape of the anatomy encountered. The rod is inserted through a loose clamp block, and the rod is placed in clamp assemblies that are received over the fixed anchor screws.
A swing bolt anchor screw is then screwed into the first vertebra adjacent the rod, and a pivot block is received on the swing bolt screw. The clamp block and/or pivot block are adjusted such that the clamp block may be engaged with a pivot on the pivot block. A set screw may then be screwed into the clamp block to secure the clamp block to the pivot. A pair of set screws are also screwed into the clamp block to secure the rod within the clamp block. Preferably, a pair of such systems are implanted on either side of the vertebrae.
During the procedure, it may be desirable to adjust the vertebrae relative to one another. Once the system(s) is (are) connected as described above, the set screws may be loosened and the rod(s), clamp block(s), and/or pivot block(s) may be adjusted, e.g., by moving the spindle(s) to adjust the height of the pivot block(s) and/or clamp assemblies on the anchor screws, by pivoting the swing bolt anchor screw(s), and/or pivoting the clamp block(s) relative to the pivot block(s). Once the vertebrae have been moved into a desired position, the set screws may be tightened, and the spindles secured in position by crimping the walls surrounding the spindles.
An advantage of this system is that the swing bolt anchor screw, pivot block, and clamp block arrangement allows the system to be adjusted about two axes, i.e., the axis of the swing bolt anchor screw and the axis of the pivot on the pivot block. However, because the system of the '166 patent is polyaxial, i.e., may pivot about multiple axes, there is greater risk of the system coming out of alignment when the patient resumes normal physical activity.
This system is also very complicated, involving six parts, including three set screws, that are mounted on each swing bolt anchor screw. In addition, because the swing bolt is threaded, an intricate spindle device is required in order to allow the pivot block and clamp assemblies to be threaded onto the swing bolt, and still control their orientation about the axis of the swing bolt. Thus, because of its complexity and many intricate parts, this system may be expensive to manufacture and/or difficult to implant.
Accordingly, apparatus and methods for stabilizing, adjusting, and/or fixing vertebrae would be considered useful.